This invention relates to a platform for fiber optic cabling for optical data multiplexing, and methods to align the fiber optic carriers to the laser sources and photonic chips.
Radiation-based, optical communications systems are increasingly popular in data centers that support the “cloud”, because of their intrinsically high data rate compared to lower frequency carriers. On the macroscale, optical data centers use thousands of optical fibers to interconnect the servers to one another. Ideally the technicians who maintain this web of interconnections could unplug one patch cable and plug in a new patch cable or a patch cable that provides a different multiplexing path much in the same way that one plugs a video cable into a television. Because the patch cable is optical and not electrical, the alignment of the myriad fibers is critical to data integrity. Also, dirt and particles can attenuate the optical path and affect data integrity. Ideally a technician could reach around to the back of the rack, disconnect the old patch cable and connect the new without being able to see the connectors.
On the microscale, optical communication applications employ a diverse set of micro-optical components. For this plurality of components, as a light beam traverses each material interface along an optical path, there is loss of optical power at each interface. This loss is generally minimized by a tedious alignment process that maximizes the system throughput and thus requires that optical power be present. Micron-level position tolerances (often sub-micron) are generally required to achieve best performance. This is further complicated by the necessity for 6-axis placement control (x, y, z, pitch, roll and yaw) and mode matching, wherein the latter refers to the numerical aperture or cone angle of a converging or diverging light beam. The refractive index change at each of the transitions causes reflections, which produce interfering scattered light and further increase losses and can be a source of noise.
Thus, complicated thin film stacks are required to form anti-reflection coatings to manage or reduce these losses. Ideally, such multilayer structures can be deposited on easily accessible surfaces for manufacturability and low cost. However, in many such systems, these multilayers are not on exposed surfaces, making them difficult to fabricate.
Supporting and disposed alongside these micro components are photonics circuits, fibers, optical waveguides, lenses, semiconductor lasers, gratings, isolators, mirrors, transparent thin films which are generally employed to create complex systems that can launch laser-generated light into a modulator that imposes a data stream onto the light. The modulated data stream is then inserted into an optical fiber. Because light from a semiconductor laser diverges from the emitting facet of the laser at an extremely high angle (20-40 degrees HWHM), a micro-lens must be precisely placed in close proximity to the laser. The placement and alignment of these components to form a laser micro-package (LMP) is described in U.S. patent application Ser. No. 14/931,883. Using a vertical grating coupler described in U.S. patent application Ser. No. 14/931,883, the light from the LMP can be injected into an optical circuit such as a photonics chip where a Mach-Zehnder interferometer imposes data on the light stream. The light stream then can be coupled into an optical fiber by butt-coupling the fiber onto a second vertical grating coupler. Generally packaging space constraints dictate that this output fiber be bent at a very small radius of curvature, resulting in yield loss, optical loss and reliability failures.
What is needed is an assembly mount or platform that provides precise datums for component registration and highly accessible surfaces to enable accurate and low cost anti-reflection coating processes. The platforms must provide microscopic datums and be manufacturable at low cost.